1. Field of Invention
The invention relates to a fan and, in particular, to a centrifugal fan.
2. Related Art
Since the present electronic products are rapidly developed towards high performance, high frequency, high speed and compactness, the generated heat of the electronic products becomes greater. However, the electronic products are unstable in the high temperature, which affects the reliability thereof. Thus, the heat dissipation has become an important issue of the present electronic products.
The fan is a common heat dissipating device for the electronic product. As shown in FIG. 1, a conventional centrifugal fan 1 includes an impeller 11 and a motor 12. The impeller 11 includes a base plate 113, a hub 111 disposed at the center of the base plate 113, and a plurality of blades 112. The base plate 113 is connected to the hub 111, and the blades 112 are disposed on the base plate 113 with respect to the hub 111 as a center. The blades 11 further includes a connecting ring 114, which is connected to a side of the blades 112 opposite to another side thereof facing the base plate 113. The motor 12 is accommodated in the hub 111 for driving the impeller 11 to rotate.
When the impeller 11 rotates, airflow enters the center of the impeller 11. Then, the rotated blades 112 force the airflow to radiately flow out of the blades 112. Since the airflow may have the counterflow, backflow, and separation phenomenon in the impeller 11, the flow field after entering the impeller 11 becomes very complicated.
In more details, since the speed of the airflow near the hub 111 is lower than that at other places, the utility efficiency of the airflow near the hub 111 is poor. If this utility efficiency is appropriately enhanced, the performance of the whole fan can be better so as to increase the heat dissipation effect. It is therefore an important subject of the invention to improve the entire working efficiency of the centrifugal fan and the impeller thereof for obtaining higher heat dissipation effect.